Method of making a cathode-grid assembly



Feb. 11, 1969 E. GRIFFITHS METHOD OF MAKING A CATHODE-GRI-D ASSEMBLY Filed Oct. 4, 1965 ATTORNEYS United States Patent O 1 Claim ABSTRACT OF THE DSCLOSURE A cathode grid assembly is made by mounting a cathode sleeve with a closed end in an insulating supporting member, thereby `forming a cathode-supporting member assembly, applying an emissive coating to the upper face of the closed end of the cathode sleeve, facing off the upper face of the emissive coating, thereby establishing a predetermined distance between the upper face o:f the emissive coating and the upper surface of the insulating supporting member, providing a spacer having a length equal to said predetermined distance plus a prescribed distance, inserting the spacer into a grid cup so that it engages the closed end thereof, introducing the cathode sleeve insulating supporting member assembly into the grid cup so that the upper surface of the insulating supporting member will engage the spacer and thus provide the requisite clearance between the upper face of the emissive coating and the closed end of the grid cup.

This invention is 'directed to cathode ray tubes and more particularly to a method of making the cathodegrid assembly of such tubes.

A cathode ray tube normally includes a plurality of electrodes forming an electron gun assembly. Such a gun includes an indirectly heated cathode in the form of a metal tube or sleeve having one end closed. The outer surface of the closed end portion is coated with an electron emissive material from which electrons are emitted when the cathode is heated by energization of a heater lament positioned within the tubular cathode.

In the conventional cathode-grid assembly, the cathode sleeve is supported by a ceramic disk suitably positioned within a control grid electrode having the form of a cup with a centrally positioned aperture in the closed cup end. The exact spacing of the top surface of the emissive coating on the closed end of the cathode sleeve with respect to the apertured end of the control grid electrode is quite critical since this distance determines the effectiveness of the action of the control grid. It is in view of the necessity of suc-h very accurate spacing between the emissive coating and the closed end of the cup-shaped control grid that the claimed methods of this invention have been developed.

It is therefore an object of this invention to provide an improved method of making a cathode-grid assembly.

It is another object to provide an improved method of making a cathode-grid assembly wherein the distance between the emissive coating on the closed end o-f the cathode sleeve and the apertured end -of the grid cup is maintained with a prescribed clearance.

Yet it is another object of this invention to provide a method of making a cathode ygrid assembly which is sirnple, inexpensive, and yet quite accurate.

It is a still 'further object to provide an improved method of making a cathode-grid assembly comprising the steps of providing a grid cup having a central aperture in its closed end, mounting a cathode sleeve with a closed end in an insulating supporting member, thereby forming a cathode supporting member assembly, applying an 3,426,413 Patented Feb. 11, 1969 ICC emissive coating to the upper face of the closed end of the cathode sleeve, thereby establishing a predetermined distance between the upper face of the emissive coating and the upper surface of the insulating supporting member, providing a spacer having a length equal to the predetermined distance between the upper surface orf the insulating supporting member and the upper face of the emissive coating plus a prescribed distance, inserting the spacer into the grid cup so that it engages the closed end thereof, introducing the cathode sleeve insulating supporting member assembly into the grid cup with the closed end of the cathode sleeve directed toward the grid cup closed end so that the upper surface of the insulating supporting member will engage the spacer and thus provide the requisite clearance between the upper face of the emissive coating and the closed end of the grid cup.

The above and other objects and advantages of the invention will become more apparent when taken in connection with the following Adetailed description and drawing showing, by way of example, one preferred embodiment of the cathode-grid assembly and wherein:

FIG. 1 is an elevational view, partly in section, showing the details of the cathode-supporting member assembly with the emissive coating applied to the closed end of the cathode sleeve; and

FIG. 2 is a vertical cross sectional view of the cornpletely assembled cathode-grid assembly.

As illustrated in FIGS. 1 and 2 of the drawing, the cathode-grid assembly 10 comprises a control grid 12 of cup shape having a closed end 14 with an aperture 16 centrally `formed therein. A cathode sleeve 18 is mounted in an insulating supporting member 20 which preferably is a ceramic disk. As illustrated, the cathode sleeve 18 may be secured to the ceramic disk 20 by means of annular beads 22 engaging the peripheral portions of the aperture in the disk to form a cathode-insulating supporting assembly 23.

The cathode sleeve 18 has a closed end 24 on which is deposited an electron emissive coating 26. A cylindrical spacer 28 having a flange 30 extending perpendicularly outward from the periphery of one end thereof is positioned within the grid cup 12 so that the unllanged end of the spacer will engage the closed end 14 of the grid cup and the flanged end Will 'be engaged by the upper surface of the insulating supporting member 20. The cathode-insulating supporting member assembly 23 is held in xed position against the spacer 28 by a suitable means which in the example illustrated comprises a anged cylinder 32 whose flanged portion 34 engages the under- 'face of the supporting insulating member 20 while the cylinder wall portion 36 is affixed to the wall portion 13 of the ygrid cup by spot welding or otherwise. A conventional lament type heater 38 is centrally positioned within the cathode sleeve 18 to provide the requisite heat for the emissive coating 26.

The aforedescribed cathode-grid assembly is more or less conventional and it is the method of making same which is the subject matter of this invention. It is well recognized that the distance designated D in FIG. 2 between the upper face of the emissive coating 26 and the lower face `40 of the closed grid cup end 14 must be closely controlled in order to provide an effective cathodegrid assembly. It is this consideration which led to this improved claimed methods of making a cathode-grid assembly.

In producing a cathode-grid assembly by a method of this invention, the grid cup 12 is provided with the cylindrical wall '13 and the closed end 14 with the aperture 16 centrally formed therein. The cathode `sleeve 18 having the closed end 24 is mounted in ceramic supporting disk 20 by means of the spaced annular beads 22 arranged in parallel planes and engaging the peripheral portions of the aperture in the ceramic disk, thus providing the cathode-ceramic supporting disk assembly 23. A specified distance B is maintained between the upper face of the closed end 24 of cathode sleeve 18 and the upper surface of the ceramic disk 20. Next, the emissive coating 26 is applied to the upper face of the closed end 24 of the cathode sleeve 18. After this, the upper face of the emissive coating 26 is ground down so as to provide a predetermined distance A between the ground upper face of the emissive coating 26 and the upper surface of the ceramic disk 20. The diiference between distance A and distance B is the distance C, the thickness of the emissive coating after grinding` Next the cylindrical spacer 28 is provided, said spacer having a length E equal to the predetermined distance A and the prescribed clearance D between the ground face of the emissive coating 26 and the inner face 40 of the closed end 14 of grid cup 12. As the next step, the cylindrical spaces 28 is inserted into the grid cup 12 so that it engages the closed end 14 thereof and encircles the aperture 16 therein. The cathode-ceramic supporting disk assembly 23 is next inserted into the grid cup 12 with the closed end 24 of the cathode sleeve 18 directed toward the closed end 14 of the grid cup 12 and within the cylindrical spacer 28, until the upper surface of the ceramic supporting disk 20 engages the flange 30 of spacer 28; thus there is provided the requisite clearance D between the upper face of the emissive coating 26 and the inner face 40 of the grid cups closed end 14. The cathodeceramic supporting disk `assembly 23 is retained in such position by any suitable means such as a tlanged cylinder 32 whose flange 34 tits up against the lower face of the ceramic disk 20. The flanged cylinder 32rnay be aixed to the grid cup wall 13 by any suitable means such as dimpling or spot welding.

The aforedescribed method presents a simple and eicient way of producing a cathode-grid assembly and yet provides an accurate spacing between the ground face of the emissive material and the inner face of the closed end of the grid cup.

4 What is claimed is:

1. The method of making a cathode-grid assembly for a cathode ray tube which comprises the steps of providing a grid cup having a central aperture in its closed end, mounting a cathode sleeve with a closed end in an insulating disk thereby forming -a cathode-supporting disk assembly wherein a specified distance is maintained between the upper face of the closed end of the cathode sleeve and the upper surface of the disk, applying an emissive `coating to the upper face of the closed end of the cathode sleeve, facing off the upper -face of the emissive coating so las to provide a predetermined distance between the upper face of the emissive coating and the upper surface .of the insulating disk, providing a cylindrical spacer having a length equal to the predetermined distance between the upper surface of the insulating disk and the upper face of the emissive coating plus -a prescribed distance, centrally inserting the cylindrical spacer into the grid cup so that it engages the closed end thereof and encircles the aperture therein, introducing the cathode supporting disk assembly into the grid cup with the closed end of the cathode tube directed toward the closed end of the grid cup and within the cylindrical spacer so that the upper surface of the insulating disk will engage the lower end of the cylindrical spacer and thus provide the requisite clearance between the upper face of the emissive coating and the closed end of the grid cup.

References Cited UNITED STATES PATENTS 1,660,506 2/1928 Hamilton 29 2,611,676 9/1952 Pohle 29-25.l3 3,240,978 3/ 1966 Krawitz 313-270 JOHN F. CAMPBELL, Primary Examiner.

RICHARD B. LAZARUS, Assistant Examiner.

U.S. Cl. X.R. 

